Composite closures typically include a metal or plastic insert disk and a plastic peripheral band. The insert disk may form a seal with a mouth of a container and usually is held in place by a vacuum within the container.
All-metal closures are an alternative to composite closures. All-metal closures, such as those on many baby food jars, include an integral top portion and skirt. The skirt may have threads or discontinuous lugs to provide mechanical engagement with a container neck finish.
The top and bottom surfaces of the metal used for insert disks or metal closures typically are coated with a solvent-based, water-based, or UV-curable coating or other composition that provides decoration, protection from scratching, adhesion for a gasket material, and/or inhibits corrosion. But because a blank for the insert disk or closure is typically cut from pre-coated sheets, the edge at the periphery of the disk (that is, the “cut edge”) is uncoated when cut.
Conventional processes either specifically coat the cut edge with a corrosion preventing material or roll it into a curl so that any corrosion is hidden by the curl. In the case of the cut-edge being rolled into a curl, while any corrosion is “hidden,” it is possible that water can be trapped in the curl promoting corrosion of the cut edge which can subsequently “bleed out” of the curl and be deposited onto the container, causing unsightly staining which is unacceptable to the end user of the package.